Thermo. Lite.

The Castelli Thermolite 13 Socks live up to the promise of their name. They're thermally insulated socks, but only mildly so, excellent for cool-weather riding conditions, and not so insulating as to be uncomfortably warm when the sun comes out or when the pace cranks up. Thermolite is a medium-density, hollow-core polyester material that promotes breathability and moisture transfer to preserve the comfort of your feet, while still insulating them enough to fend off the chill of fall days. The midfoot is supported by an anatomic band of fabric that prevents cramping and hotspots. The socks have a 13-centimeter cuff, come in the sizes S/M, L/XL, and XXL, and in the colors Black or White.

Comment on Benoit B.'s review:

Warm & Comfortable

Familiarity:
I've used it several times

These socks were warm and comfortable but they only lasted one season. I think I should have gotten at least two. However, they never lost their stretch o comfort. They just developed a hole near the toe. I rarely tide below 50 deg F and I use a toe shoe guard when it gets colder. These socks work well for me down to about 55 deg and then I start wanting the guard. I have probably worn them 50 or 60 times on rides over 30 miles.